1. Field of the Invention
The present invention relates to a method for identifying the attenuated varicella virus Oka strain. More particularly, the present invention relates to a method for identifying the attenuated varicella virus Oka strain or a strain derived therefrom capable of functioning as an attenuated varicella live vaccine virus, and an isolated virus strain which is substantially the same virus strain as identified as the attenuated varicella virus Oka strain or a strain derived therefrom by the above method. The present invention also relates to an attenuated varicella virus Oka strain antigen. The present invention further relates to a pair of novel primers which are advantageously, effectively usable in the method of the present invention.
2. Prior Art
As is well known, attenuated live varicella vaccines used today are manufactured from a seed strain of varicella-zoster virus (hereinafter, frequently referred to simply as "varicella virus") which is a virus derived from the attenuated varicella virus Oka strain (see Examined Japanese Patent Application Publication No. 53-41202 and U.S. Pat. No. 3,985,615), and the attenuated live vaccines are used widely throughout the world {Requirements for Varicella Vaccine (Live) Adopted 1984: WHO Technical Report Series, No. 725, pp. 102-124, 1985}. To ensure the safety and effectiveness of the vaccine, the number of passages of a virus used for producing the vaccine is under the control of a seed lot system, taking into consideration the potential genetic mutation which is likely to occur during the passage. That is, the manufacturers are under an obligation to produce varicella vaccines only from the virus derived from the approved seed virus for the live varicella vaccine, wherein the number of passages of the virus is not more than 10 as counted from the approved seed virus which is counted as 0 passage. In other words, the quality control and quality assurance of the attenuated live varicella vaccine rely upon the fulfillment of the seed lot system by the manufacturers, and the quality of the vaccine has not been determined by a direct genetic analysis of a seed virus genomic DNA or a vaccine virus genomic DNA.
Further, from the viewpoint of epidemiology which involves a tracing of the effects of a varicella vaccine and a post-market surveillance (PMS), the virological difference between the fresh wild-type strains isolated from the naturally infected varicella patients and the vaccine virus strains derived from the above-mentioned Oka strain needs to be determined, and various methods have been attempted for determination of the virological difference. Since the gene of a VZV genome and the structure of the gene were reported (Journal of General Virology, 67, 1759-1816, 1986), various determination methods of the virological difference based on the differences between the properties and characteristics of the strains, such as the difference in DNA sequence between the different VZV strains (Journal of Virology, 59, 660-668, 1986), the difference in the absence or presence of a restriction enzyme PstI cleavage site (Japanese Journal of Experimental Medicine, 59, 233-237, 1989), the difference in RFLP (restriction fragment length polymorphism) of the PCR (polymerase chain reaction) product (Journal of Virology, 66, 1016-1020, 1992), and the difference in the absence or presence of a restriction enzyme PstI restriction site which is taken in combination with the difference in RFLP of the PCR product (Journal of Clinical Microbiology, 33, 658-660, 1995). However, all of these methods are not sufficient and cannot be used for exact identification of the Oka strain.
In other words, for quality control and quality assurance of the vaccine and from the viewpoint of epidemiology which involves a tracing of the effects of the vaccine and a PMS, it is critically important to identify or determine the above-mentioned attenuated varicella virus Oka strain or a strain derived therefrom capable of functioning as an attenuated varicella live vaccine virus (which Oka strain or a strain derived therefrom can be used as an active ingredient of an attenuated live varicella vaccine). However, a method reliable for such identification or determination has not been established, and a development of such a method has been earnestly desired in the art.